The present invention relates to a torque grease which is used to give lubricity for the rotation of a rotary shaft of, for example, a rotary variable resistor or a dial in an electronic component or an audio device, and to impart a feeling of a high-grade article owing to the rotary torque of a bearing to a person who rotates the shaft.
It is well known in the art that greases, such as a mixture of polyisobutene and a thickener or a mixture of polyisobutene, a mineral oil and a thickener, are useful to give lubricity for a rotating shaft of a rotary volume dial in an electronic component, an audio device, or the like, and to produce a rotating shaft having the feel of high-grade article.
However, these greases have disadvantages in that the viscosity of the polyisobutene may suddenly decrease resulting in bleeding of the grease from the coated area, or the polyisobutene can decompose to cause hardening of the grease. Also, when the grease is allowed to stand in the atmosphere above 100.degree. C. for a long time, or the grease is allowed to solidify in the atmosphere near 0.degree. C., rotation of the resistor dial becomes difficult or even impossible.
Some attempts have been made to overcome the disadvantages described above. For example, silicone greases having moderate tackiness as described in Japanese Patent Laid-Open No. 66552/1975 and No. 43171/1978. More particularly, Japanese Patent Laid-Open No. 66552/1975 discloses a silicone grease comprising a polydiorganosiloxane, consisting of R.sub.3 SiO.sub.1/2 units, R.sub.2 SiO units and SiO.sub.2 units, and a thickener; Japanese Patent Laid-Open No. 43171/1978 discloses a silicone grease comprising a polydiorganosiloxane, a polyorganosiloxane composition consisting of R.sub.3 SiO.sub.1/2 units, RSiO.sub.3/2 units and SiO.sub.2 units, and a thickener, wherein R is a group selected from alkyl radicals, alkenyl radicals and aryl radicals.
These silicone greases have improved operating characteristics at low-temperatures as compared with the polybutene greases, but the operating characteristics are not sufficient as yet. Furthermore, the silicone greases have disadvantages in that the torque is decreased and finally the rotating shaft is abraded to become inoperable (or "seize up") when the rotary resistor dial is operated for a long time.
Now it has been found that the lowering of the operating characteristcs and the torque at low-temperatures as described above is caused by the polyorganosiloxanes consisting of R.sub.3 SiO.sub.1/2, RSiO.sub.3/2, R.sub.2 SiO and SiO.sub.2 units used as a base fluid in conventional silicone greases.
That is to say, the polyorganosiloxane consisting of R.sub.3 SiO.sub.1/2, RSiO.sub.3/2, R.sub.2 SiO and SiO.sub.2 units is used to enhance the tackiness of silicone greases, but at low temperatures it tends to crystallize, so that rotary operation becomes difficult and the rotating shaft is abraded upon operating it for a long time to result in seizing up.